


Determined Alphys AU

by yourecool



Category: Undertale (Video Game)
Genre: Alphys fighting Frisk isn’t actually gonna be the main focus, Body Horror, DT Alphys AU, Don’t worry, F/F, Undertale Genocide Route, itll get focus though, no beta we die like men
Language: English
Status: In-Progress
Published: 2019-10-23
Updated: 2020-04-09
Packaged: 2020-12-31 16:57:41
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence, Major Character Death
Chapters: 3
Words: 3,240
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21149093
Author URL: https://archiveofourown.org/users/yourecool/pseuds/yourecool
Summary: Alphys injects herself with DT and goes to fight the player instead of Undyne.





	1. Decision

“This way, hurry.”

Undyne lead a small group of monsters into the lab and down the hall, where Alphys and a few others stood by the elevator, waiting for them. Parents and spouses, mostly, hoping to find a child or a partner among the lost, frightened faces. There were also one or two monsters present who had volunteered to act as Alphys’ assistants. Alphys greeted them all with a shaky smile, and strained as it was, it seemed to put at least a few of the survivors at ease. 

“We’ll send you down in groups of five,” Alphys said. She seemed to be doing her best not to acknowledge that there were only eight monsters this time, excluding the four who had been waiting with her. “Once everyone is safely gathered in the True Lab, I’ll explain the situation best I can. Feel free to ask if you have any questions, or if there’s someone you’re looking for. If they’re not already in the True Lab, Undyne will keep an eye out for them during her next sweep.” Some of the monsters glanced over at Undyne. She gave them a nod. 

Despite her statement about only taking five at a time, Alphys ushered all eight monsters into the elevator at once. As they went, Undyne heard her telling them, “once you get down you’ll be greeted by the amalgamates… try not to panic. although they may look frightening, I promise they’re harmless.”

Undyne stayed back and waited. Twenty minutes later, The elevator dinged again. There was a whirring sound, and then Alphys stepped back out and came over. She gave Undyne a questioning look.

“I’m going to do another sweep.” Undyne told her. I haven’t checked all of waterfall yet—there might be someone hiding in the caves that I missed.” 

Alphys took a moment to process that. She let out a shaky breath, and took Undyne’s hand in hers, threading their fingers together, careful to be gentle and avoid pulling at the thin vestigial webbing between Undyne’s fingers. She was silent for a bit. 

“Alright,” She said. “Be safe, Undyne.” And she let go of her hand.

——

Undyne made it back. She brought a Temmie and Grillby with her, as well as some others. This time there were only five, and only two people there waiting.

“Marylily fell down,” Alphys informed Undyne in hushed tones. “She’s not the only one.”

There were heavy bags under her eyes. 

——

“What are you doing?” Alphys said, and Undyne’s breath caught in her throat. She turned around. Alphys was standing in the doorway, an unreadable look on her face. She looked Undyne over, and then her vision caught on a glint of red light and her eyes went to the syringe in Undyne’s hand. Her expression shifted to one of...sorrow? Understanding? Horror? “Oh,” she said. Undyne was silent. 

“...I understand why,” Alphys told her after a moment. “I can’t really think of a way to beat the hum— the whatever it is, otherwise. But, I told you about the amalgamates, right?” Undyne’s fist tightened around the syringe. Sudden frustration flared up in her chest, and she snapped at Alphys. “I don’t give a fuck about that, Alphys! People are DYING, I can’t just, I can’t,” Undyne snarled, struggling to find the right words, frustrated with Alphys, with herself, with everything. “What else am I supposed to DO?!?” She shouted, half angry, half desperate. Alphys stumbled back, her calm slipping, and Undyne saw her own fear and anger and desperation reflected in Alphy’s eyes. She stopped.

“...What are we supposed to do?” She repeated, suddenly exhausted. Alphys looked like she wanted to cry. Undyne felt like dirt for putting that expression on her face.

“...I don’t know.” Alphys admitted, voice small. “I just…” she ran a hand down her face. “Don’t go injecting yourself all willy nilly, Undyne, I tried that with the amalgamates and it didn’t fix a thing.” Alphys took a few breaths to compose herself. She thought for a moment. “Look, I know more about Determination than just about any monster in the underground. I may not have managed to fix my mistakes,” she swallowed, “but I discovered a lot about how determination works. There might be a way to take DT safely. If I could...Just, give me time to work on it.” Undyne frowned at her. “Are you sure the rest will be ok with this? I thought—“

”I’m not going to use monsters. I won’t need any test subjects for this.”

Undyne studied Alphys for a moment. “...ok.” She conceded, and set the syringe back down on the table. They left the lab together.

——

A few weeks later, Alphys snuck a folded note under Undyne’s pillow, double checking while she did to make sure Undyne was really asleep.

She slipped out unnoticed.

Alphys took the elevator up and out of the True Lab, made her way down the hall of the lab, and stepped out into the warm night air of Hotland. It was utterly silent and still. There wasn’t a single monster in sight. The ‘human’ hadn’t even come to Hotland yet, Alphys knew. She’d been monitoring it.   
It didn’t feel that way.

It was terrifying, how dead the air was. As if there wasn’t a single living thing left in the entire world. Was this what Undyne felt, every time she went out on a sweep?

Alphys shook her head and refocused. Now wasn’t the time to think about that. She came here for a reason.

She pulled the DT syringe out of her pocket.

She had taken safety measures, gone several lengths to ensure this would work. She had already injected herself with small doses of DT during testing, in a more controlled setting. She had been fine so far. No melting. There wasn’t any reason to worry, but she still found herself hesitating, taking her time checking the liquid for air bubbles, prepping her arm, finding a big enough chunk in her scales. When she reluctantly finished with that and went to inject herself, the needle froze just inches from her arm. Her hand shook.

Was it worth the risk, really?

Alphys took a deep, fortifying breath. She remembered the haunted, grieving monsters in the True Lab, the missing family members and friends they spoke of. The ones that had fallen down in their despair. How fewer and fewer survivors were brought back with each sweep. She thought of Undyne. 

Her fear vanished.  
It was replaced with utter rage.

She slid the needle in, and slammed the plunger down.


	2. Flashback time

**Summary for the Chapter:**

> This one is kind of messy and I didn’t really proofread it well but here it is! I’ll fix the mistakes later

Alphys had been the first to know what was happening, mostly because she had surveillance cameras scattered all across the underground, keeping watch for humans. She’d been curled up in a swivel chair with her tail wrapped around her feet, stationed in front of the monitor, keeping half an eye on the video feed and at the same time flipping through a new volume of Mew Mew Kissy Cutie while messily eating a bowl of instant ramen, trying not to think too hard about the call she just got from the snowdrake family. Then out of nowhere the doors to the ruins opened for the first time in years, and a human had stepped out into the snow. Alphys had only ever seen humans in photographs before.

She had always wondered if humans were really all that bad. The King and Queen’s adopted child had seemed very nice in the stories, and despite what everyone said, Alphys doubted they were just the exception to some rule.

The human had dust on their sweater. 

...Of course, the human had probably been attacked by hostile monsters. They might not have always been able to show mercy, Alphys told herself. But knowing this human had killed someone didn’t sit well with her, and she shifted anxiously in her seat. Who did they kill? She wondered. Why?

Alphys really loved the things humans created. Not just their manga—the things they made were always beautiful or fun or useful or full of valuable knowledge. It felt fulfilling to unearth something new and exciting buried among the piles of human garbage that washed ashore in waterfall. Dumpster diving was still her favorite pastime, even with Bratty and Catty gone and after all these years, and the treasures she collected there helped her make it through especially bad days when there was nothing else that could. The Dump was where she first met Undyne.

It was always hard to reconcile her love for human culture with the fact that monsters were imprisoned in the underground by humans, after a war between the species during which countless monsters were wiped out. 

For some reason it really bugged her that she couldn’t see the human’s expression. Her camera was at the wrong angle for it, so she just had to hope she’d get a better look at their face in another area. Setting aside the bowl of ramen and putting down her manga, she watched the monitor carefully.

Alphys’s cameras weren’t everywhere, so she inevitably lost sight of the human every once in a while. She felt weirdly nervous and jittery during the periods when they weren’t visible, when she had no way to tell what they were doing. Maybe it was just her mind playing tricks on her, but the sweater always looked dustier when it reappeared. 

Then Alphys saw the human kill Dogamy and Dogaressa. 

As much as it horrified and upset her, Alphys could almost understand Dogaressa. The two dogs had attacked the human first, with the intent to kill, and even if Dogaressa was a friend of Alphys’s, even if the human didn’t hesitate for even a second, or seem to feel any guilt whatsoever over killing her, they were still defending themselves when they did it. 

But after Dogaressa died, Dogamy just...gave up. He whimpered weakly and stopped trying to fight, making no effort to even defend himself. He just sat, taking blow after blow. And the human didn’t stop when they saw this, even though Dogamy was no threat to them now, even though they could leave and he wouldn’t stop them, attacking him relentlessly with their toy knife until Dogamy’s soul shattered and he fell apart into dust and

Alphys turned off the monitor, shot out of her chair, bolted for the trash can and puked. When she was done, she fumbled for her phone with shaking hands and called King Asgore to warn him. 

There was a murderer loose in the underground.

——

“I went looking for Papyrus’s battle body,” Undyne told her, “found it right at the spot where that creature killed him. His remains weren’t there though—I saw footprints. I’m pretty sure his bro came back for his dust.” Undyne ran a hand through her hair, and sighed. “I looked everywhere, but Sans was nowhere to be found. I couldn’t locate Doggo either.” 

Undyne’s face was drawn. She looked pale and worried. Alphys reached out and held her hand, offering what comfort she could. 

She was pretty worried herself. Doggo may have been a bit of a grump but he was a loyal guardsman, and he was a good friend to Undyne. Alphys didn't know Sans particularly well, but they were both scientists, and although they were interested in different fields, they met up sometimes to compare notes. And he was Papyrus’s brother. Papyrus would have wanted him to be safe.

“There’s also this kid I’m searching for.” Undyne said, “Monster Kid. She used to follow me around Waterfall during patrols.”

“Waterfall?” Alphys asks, eyes widening. Undyne nods grimly. 

The human was in Waterfall.

——

It wasn’t a human, those who had seen it agreed. Or it was human in only the vaguest sense of the word. An older Aaron, who had actually been present during the war, explained. “Look at the pictures of the human soldiers in the history texts. Look at their faces. What do you see?” 

The faces of the humans in the pictures were frightful, their expressions twisted with rage and hate, gleeful bloodthirst, fear, disgust. The only smiling human was, again, the King and Queen’s child, Chara. A soft, gentle smile. It looked happy at first glance, but Alphys had always thought there was something almost haunted in their expression.

She thought back to the last time she had a clear view of the not quite a human’s face, although remembering Dogamy and Dogaressa still made her feel queasy. It had held absolutely no emotion during the entirety of the fight, remaining expressionless even as the dogs crumbled to dust in front of it. No surprise, no guilt, no fear, not even joy over its victory. It’s eyes shone with determination, and it’s face was utterly blank.

“It’s almost human,” the Aaron told them, “but something’s missing.”

——

After the news about Snowdin and Papyrus’s death an evacuation order was issued. Hotland, the Core, and New Home were all evacuated first. They got as many people as they could out of Waterfall, but the almost-human was fast, and ruthless. The bravest Royal Guard members, lead by Undyne, managed to get to Snowdin unimpeded, and gathered up the remaining survivors there. Most of them made it back safely, but a couple of monsters were lured away from the group by Shyren’s concert, and were too slow to escape after the almost-human killed her and sprung its trap.

Alphys knew that the True Lab, which was fortified and had a backup generator, emergency food stores, and a fully equipped mini hospital, was the best option that they had for a shelter. 

She knew what they would find in there, but there was no _time_ to hesitate over this—before she could second guess her decision, Alphys announced that she was opening the True Lab’s doors, despite knowing that in doing so she would be revealing all of her darkest, most shameful secrets.

This meant telling everyone about the Amalgamates.

A surprising amount people forgive her for her mistakes. Of course there were a few who were (rightly) angry, who yelled at her for hours, who wouldn’t even look at her after what she had done... but so many others stepped forward in her defense, saying that while it didn’t excuse her actions, she had spent years working to fix the damage she had caused and had helped the amalgamates to the best of her ability, pointing out also that she had opted to expose her darkest secrets to everyone rather than deprive them of a safe shelter. 

Alphys knew she was lucky—she deserved far worse than she was getting.

Knowing that didn’t make it hurt any less when a few monsters refused to shelter in the True Lab at all, saying they would rather die at the hands of the almost human than accept the protection of a monster almost as bad as it was.

Alphys could only pray that they survived this, same as she did every other monster who, for whatever reason, chose to stay behind.

——

Alphys told Undyne first. She explained about the experiments with DT and the fallen monsters, the promise she made to return their dust to their families. She told her about waking up one morning to find all the fallen monsters, who had been on the threshold of death the day before, up and walking about, seemingly cured. She had thought it was a miracle then. Bewildered but happy, she had called up each of their families to tell them the good news, and got ready to send them all home. 

Then a droopy looking Snowy limped over to her, accompanied by Vegetoid, who was helping her stay upright as she walked. She complained that she wasn’t feeling very well, and could going home wait a bit? Alphys started to respond. At that moment, Snowy started to melt, and Vegetoid began to melt with her, and their forms melted and ran together, and then Alphys heard screaming from the other room.

She hadn’t been able to save any of them. Their families called asking about them, when they would return, and Alphys didn’t know what to say.

So she lied.

——

When the story was over, Undyne reached over and pulled Alphys into a hug.

Alphys had been prepared for the worst. She knew Undyne would be absolutely justified in hating her. She knew that she deserved it. 

But Undyne forgave her.

Undyne forgave her.

**Notes for the Chapter:**

> Oh, almost forgot! Here’s a link to some art I did for this AU on tumblr  
https://diddlydarndoodles.tumblr.com/post/183175246124/i-have-now-redrawn-my-old-undertale-fanart-gaze


	3. Test 1

**Summary for the Chapter:**

> Alphys records the effects of DT.

The first time Alphys injected herself with DT, she wasn’t prepared for what it would feel like.

She’d made preparations, of course. Alphys wasn’t reckless or stupid enough(or desperate enough, yet) to just inject herself with pure Determination straightaway. She had distilled the substance with water-- the current ratio was about 86% water, 14% DT, but she planned to increase the concentration slightly every time she took it. She had set up a diet plan, adjusted to contain more solid foods and fewer magic based foods, which would hopefully increase the physicality of her form. 

Still, she was nervous. 

Adjusting her glasses anxiously, Alphys marked the date in her notebook--tuesday, february 3rd, 9:43am--slid on a pair of rubber gloves, and picked up a fresh syringe with ginger claws. She tapped it a couple of times to remove the air bubbles, and slid it in through a tiny chink in between the scales of her arm.

It was as if she had been struck by lightning.

Colors sharpened into focus. Alphys was instantly hyper aware of herself and of the space she occupied. For the first time, it occurred to her how malleable both those things were. 

Alphys hadn’t quite registered exactly how tired she had grown over time, but now her prior exhaustion was glaring in its utter absence. Now her soul was electrified, and she was brimming to burst with an energy that teetered on the edge of overwhelming. 

She felt like she should be bouncing off the walls, jittery and unfocused with the force of it, but it was so simple now to just…  _ decide _ to stay calm. Easy. 

Suddenly everything was so easy. Alphys had absolute control over herself, in a way she hadn’t thought she was capable of. All of the sudden she was  _ powerful _ .

With an ease that felt utterly alien, Alphys shifted her focus back to the task at hand. 

She documented her observations in the empty notebook she had brought for just that purpose, listing the effects she’d noticed so far, and describing how she’d felt after the injection was administered, making sure to record the dosage and level of concentration as well.

Then she went back to experimenting. 

That first DT high lasted several days, during which she holed up in her lab studying and experimenting with DT. During that time her focus was unwavering. Not once did her thoughts wander from the task at hand. 

Eventually, exhaustion began to set in. Her limbs grew sore, and she became aware of dried sweat coating her skin. Alphys blinked blearily, rubbing her head--she had a splitting headache all of the sudden, and she  _ stank _ . What time was it? 

Alphys glanced over at the clock on her desk. And froze. It was 8:50pm on a Friday, she realized suddenly, and four days had gone by--and she hadn’t slept during all that time.

Monsters couldn’t survive four days of no sleep.

And yet, here she was.

**Notes for the Chapter:**

> this one's a bit short.


End file.
